1. Field of the Invention
The present invention relates to the field of impulse hammers and, more particularly, to a novel such hammer incorporating means for allowing manual switching between a selection of operational ranges.
2. Brief Description of the Prior Art
In the past, impulse hammers have been used to shock structures and machines into motion for the purpose of analyzing behavior in terms of frequency characteristics. Impulse hammers incorporate rigid quartz for sensors mounted in a head carried on the end of a handle in order to produce output voltages exactly analogous to force pulses created when a test structure is struck by the hammer. The generated voltage pulse defines mathematically the input or "forcing" function. Resultant motion is sensed by accelerometers mounted elsewhere on a test structure and, in some instances, spectrum analyzers, computers and other instrumentation are responsive to these output signals so as to perform modal analysis, graphically display transfer functions and to search for destructive or annoying resonances.
Difficulties and problems have been encountered when employing conventional impulse hammers which stem from the fact that three or more different hammers are often necessary in order to cover a dynamic range of operation. For example, depending upon the size of the test structure, forces as low as one pound or as high as 5,000 pounds may be necessary for optimum results. Also, difficulties have been encountered in conventional hammers wherein the cable or wiring from the load cell transducer in the head of the instrument or hammer is generally external and is cumbersome, makes the handling of the instrument difficult to use. With some prior impact hammers, a gain amplifier is employed which determines the hammer sensitivity and thus the range of the device. Such a practice is not conducive to accuracy inasmuch as undesired noise levels are magnified or amplified and cause distortion in the ouptut signal. Still further problems with conventional impulse hammers reside in the lack of overload protection to prevent adding more negative feedback from affecting discharge time constants and compromising pulse fidelity.
Therefore, a long standing need has existed to provide an improved impulse hammer having selection means for deriving a plurality of sensitivity selections within a wide range of force inputs so as to eliminate the need for different fixed range hammers. Also, a need is present to provide a sensitivity means in an impulse hammer which is not dependent on a gain amplifier which would normally amplify noise levels and which would provide overload protection for the circuit involved.